If for A.P., T₂₅ — T₂₀ = 15 then d =

We know that, T_n = a + (n – 1)d

So we have, T₂₅= a + (25 – 1)d

⇒ T₂₅= a + 24d

Now we have, T₂₀= a + (20 – 1)d

⇒ T₂₀= a + 19d

It is given that, T₂₅ — T₂₀ = 15

So we can say that,

⇒ 15 = [a + 24d] – [a + 19d]

⇒ 15 = 5d

⇒ d = 3

∴ the correct option is (a).